Polymeric materials, such as thermoplastic polyolefin (TPO) and reaction injected molding urethane (RIM), are useful in many applications, such as automobile parts and accessories, containers, household appliances and other commercial items. It is often desirable to coat articles made from such polymeric materials with organic coating compositions to decorate or protect them from degradation when exposed to atmospheric weathering conditions such as sunlight, moisture, heat and cold. To achieve longer lasting and more durable parts, it is important for the coatings to be tightly adhered to the surface of the article.
Polymeric substrates made from a variety of thermoplastic and thermosetting materials have widely varying surface properties, including surface tension, roughness and flexibility, which make strong adhesion of organic coatings difficult, particularly after aging or environmental exposure of the coated polymeric materials. To facilitate adhesion of organic coatings to polymeric substrates, the substrate can be pretreated using an adhesion promoter layer or tie coat, e.g., a thin layer about 0.25 mils (6.35 microns) thick, or by flame or corona pretreatment. For automotive applications, it is important that the coating composition and/or adhesion promoter layer is resistant to fuel damage, i.e. maintains good adhesion of the coating to the substrate even if fuel is accidentally spilled onto the coated substrate.
Typically, adhesion promoter layers used on TPO surfaces contain chlorinated polyolefins, some examples of which are described in U.S. Pat. Nos. 4,997,882; 5,319,032; and 5,397,602, herein incorporated by reference. However, chlorinated polyolefins provide some processing limitations. For example, while chlorinated polyolefins are soluble in aromatic solvents, THF, and chlorinated solvents, they are not readily soluble in solvents such as alcohols, ketones, or esters which are preferred for use in coating compositions. Further, conventional chlorinated polyolefins typically have no curing or crosslinking sites and therefore must be used at high molecular weights to have a positive effect on coating strength.
Coating compositions that exhibit acceptable adhesion directly to polymeric materials, such as TPO and RIM, without the use of separate adhesion promoter layers or tie coats have been developed. For example, polyolefin diols have been used in coating compositions to improve adhesion to polymeric substrates without the use of separate adhesion promoter layers or tie coats. For example, U.S. Pat. No. 6,001,469, herein incorporated by reference, discloses a coating composition containing a saturated polyhydroxylated polydiene polymer having terminal hydroxyl groups.
U.S. Pat. No. 5,863,646, herein incorporated by reference, discloses a liquid adhesion promoting coating composition having a blend of a saturated polyhydroxylated polydiene polymer and a chlorinated polyolefin.
Coating compositions having reacted adhesion promoters have also been developed. For example, U.S. Pat. No. 5,135,984 discloses a coating composition having an adhesion promoting material obtained by reacting a chlorinated polyolefin, maleic acid anhydride, acryl or methacryl modified hydrogenated polybutadiene containing at least one acryloyl group or methacryloyl group per unit molecule, and organic peroxide.
JP 6-16746 discloses a resin coating composition having either a polydiene and acryl-based oligomer or a polyester-based oligomer grafted onto a chlorinated polyolefin.
While these known adhesion promoting compositions are generally acceptable for commercial applications, they tend to either have good adhesion to polymeric substrates with poor to moderate fuel resistance; good fuel resistance but with commercially acceptable adhesion to only a narrow range of polymeric substrate types; or good adhesion and good fuel resistance but only at high levels of chlorinated polyolefin resulting in high VOC.
It would be desirable to provide an adhesion promoting agent that could be used either in an adhesion promoter layer or as an ingredient in a coating composition that improves coating adhesion to polymeric substrates and also provides adequate fuel resistance for automotive applications.